The overall objective of the proposed studies is to continue microbiological and biochemical analysis of unique characteristics which allow specific bacteria to survive in the human oral cavity, interact and become a part of dental plaque, and initiate dental caries on the tooth surface. The specific objectives of these studies are: 1. To utilize purified and characterized glucosyltransferases and other glucan-binding components from Streptococcus mutans to determine the mechanism of water-insoluble adherent glucan production by this bacterium. Mutants which produce decreased and elevated levels of glucosyltransferase will be utilized in these studies; 2. To determine the role in glucan production from sucrose of the endohydrolytic dextranase produced by S. mutans. This will be accomplished utilizing mutants which we have isolated which are unable to synthesize this enzyme in an active form; 3. To continue evaluation of the role of indigenous dextranase-producing oral bacteria in regulating the retention in the mouth and cariogenicity of glucan-producing oral streptococci and lactobacilli; 4. To analyze in detail the molecular structure of the bacterial and host factors involved in isotypic and heterotypic oral bacterial cell-cell interactions and oral bacterial cell-solid surface adherence reactions. Several sensititve, quantitative and facile in vitro plaque-forming assays will be utilized in these investigations. Emphasis will be placed on defining the interactions between oral bacteria which enhance or suppress their ability to become a part of, and to proliferate in, dental plaque. The long-term goal of this research is to define the interactions involved in regulating the microbial content of the oral cavity which could be used to develop a caries control measure based on selective inhibition of specific "caries-inducing" microorganisms.